In the oilfield industry, it is common to install wells that extend laterally from a primary (sometimes vertical) well. These lateral wells extend into the underground formation surrounding the primary well and therefore increase the effective drainage area around the primary well.
Several techniques are currently used to drill and complete lateral wells. In cased primary wells, lateral wells are typically drilled through windows provided in the casing. These windows are often milled through the casing after it has been cemented in the primary well. In order to cut a window in the casing, a device that includes a packer and a whipstock is inserted into the primary well. The packer is set at a location that is immediately downhole of the desired location of the window and in such an orientation that the concave face on the whipstock faces the window. Thereafter a milling device is inserted into the primary well and the concave face on the whipstock deflects the milling device laterally towards the casing and thus facilitates milling at the desired location for the window.